<?php

header('Content-Type:text/xml');

$zip = (string)$_GET['zip'];
$walk = '';
if($zip > 0)
{
  $lines = file('data.xml');
  foreach ($lines as $line_num => $line) 
  {
    if(substr_count($line, ' zip="' . $zip . '"') > 0)
    {
      $walk = $walk . $line;
    }
  }
}

echo <<<XML
<walks>$walk</walks>
XML;
?>